A Long Term Evolution (LTE) is a cellular communication system that is considered in a 3rd generation partnership project (3GPP) as a successor of a W-CDMA. An LTE network is also called an evolved universal terrestrial radio access network (E-UTRAN).
Uplink radio resources in the LTE are allocated by dividing a plurality of resource blocks (RBs) to a plurality of mobile stations. The resource block is a resource element in which a frequency domain is divided in a unit of 180 kHz (12 subcarriers, each interval between subcarriers being 15 kHz), and a time domain is divided in a unit of 1 milliseconds. Note that the allocation control of the resource blocks is called “scheduling”.
The scheduling of the uplink radio resources is performed by a base station. The base station measures reception quality of a reference signal (SRS: Sounding Reference Signal) transmitted from the mobile station, and determines, based on this reception quality, the number of resource blocks, hopping patterns, radio modulation scheme (QPSK, 16 QAM or 64 QAM), and the like allocated to a physical uplink shared channel (PUSCH) used by each mobile station to transmit user data.
The transmission power of PUSCH depends on the maximum transmission power of the mobile station and the number of resource blocks that are allocated. Thus, the base station notifies the mobile station of allowable maximum transmission power P_EMAX in advance, and performs scheduling of the uplink radio resources in consideration of the maximum transmission power P_EMAX notified to the mobile station. The mobile station receives the result of scheduling performed by the base station, and transmits the uplink signal using the resource block specified by the base station.
The transmission power when the mobile station transmits the PUSCH is determined based on the number of resource blocks (frequency band) allocated to the PUSCH, the magnitude of the path loss of the downlink estimated by the mobile station, and the like. The total transmission power of the mobile station is controlled so as not to exceed a maximum transmission power P_CMAX imposed on the mobile station. The mobile station sets smaller one between the allowable maximum transmission power P_EMAX notified from the base station and a transmission power upper-limit value P_UMAX associated with a power class of the mobile station as the maximum transmission power P_CMAX.
See specifications of the 3GPP listed as Non-patent literatures 1 to 3 for more details of the scheduling of the uplink radio resources and the uplink transmission power control in the LTE described above. Specifically, Non-patent literature 1 includes the inclusive specifications regarding the mobile station of the LTE system. In particular, it includes the specification of the power class of the mobile station, and the specification of the transmission power upper-limit value P_UMAX for each power class. Further, Non-patent literature 1 specifies that smaller one between the maximum transmission power P_EMAX allowed by an upper layer and the transmission power upper-limit value P_UMAX corresponds to power class should be selected as the maximum transmission power P_CMAX actually set in the mobile station.
Non-patent literature 2 includes specifications regarding a physical layer of LTE. More specifically, it includes specifications regarding the uplink transmission power control such as a definition expression to determine the transmission power of PUSCH.
Non-patent literature 3 includes specifications regarding a transmission timing of a power headroom report (PHR) transmitted from a mobile station of LTE to a base station. “Power Headroom” is calculated as a difference between a maximum transmission power P_CMAX that is actually set in the mobile station and a current transmission power of the mobile station. In short, “Power Headroom” means the “transmission power margin” of the mobile station with respect to the maximum transmission power P_CMAX.
Further, Patent literature 1 discloses the following two points:    (i) a mobile station notifies a base station of a transmission power margin (i.e. power headroom); and    (ii) the base station performs scheduling of uplink radio resources in consideration of the transmission power margin notified from the mobile station.
Further, Patent literature 2 discloses the following points (i) to (v):    (i) a mobile station transmits a transmission power upper-limit value P_UMAX specified according to the power class of itself to a radio network controller (RNC) that manages uplink radio resources;    (ii) the RNC selects smaller one between a maximum allowable transmission power P_EMAX allowed for the mobile station and the transmission power upper-limit value P_UMAX received from the mobile station, thereby determining a maximum transmission power P_CMAX that is actually set by the mobile station;    (iii) the RNC notifies a base station of the maximum transmission power P_CMAX of the mobile station that is determined;    (iv) the mobile station transmits a transmission power margin (i.e. power headroom) to the base station; and    (v) the base station calculates a current transmission power of the mobile station using the transmission power margin received from the mobile station and the maximum transmission power P_CMAX of the mobile station received from the RNC, and performs scheduling of the uplink radio resources.